The big picture: Plants evolved from green algae


  • Cyanobacteria & protist made landfall ~1.2 bya
    • plants, fungi and animals ~500 mya
    • first forests 385 mya


  • Plants evolved from green algae
    • Several key ‘shared traits’
    • WHAT DO YOU THINK THEY ARE?


  • Plants support all life on earth
    • Oxygen to breath
    • food to eat
    • new habitats

Protists that share traits with plants


  • Dinoflagellates - unicellular aquatic
    • some are photosynthetic
    • haploid dominate life cycle


  • Brown Algae - large multicellular aquatic
    • AoG life cycle
    • identical haploid and diploid life cycle
    • photosynthetic


  • Diatoms - unicellular aquatic
    • all are photosynthetic
    • diploid dominated life cycle










Not ancestral to plants!

Green Algae (Oedogonium)


  • Sister group to land plants
    • all are photosynthetic
    • marine and freshwater
    • single and multi-cellular
    • broad, thick filaments
    • some have AoG
    • evolved around ~750mya


  • Reproductive features:
    • Oogonia = egg containing cell
    • Antheridium = sperm containing cell

Molecular evidence points at charophytes as plant ancestors

Charophytes (freshwater green algae)


  • Freshwater species


  • Transition from water to land starts with Charophytes
    • freshwater habitats may have dried
    • a population eventually lived above water line


  • More shared traits with land plants:
    • circular protein rings in plasma membrane
    • make cellulose fibers in cell wall
    • swimming sperm with similar structure
    • phragmoplast (something with cell division)
    • ROS genes

Living on Land: The Wild Wild West

Land plants are a monophyletic group

Shared Traits define plant evolution

Multi-cellular, Dependent embryos (placental transfer)

Waxy cuticle and stomata

Multi-cellular Gametangia

Photosynthesis with unique pigments (chlorophyll A & B)

Unique cell walls




  • Cells walls made of cellulose
    • not unique to plants


  • Pectin to fortify cell walls
    • unique to plants


  • Produce cells walls in unique way
    • at end of mitosis

Alternation of generations

First plant group: non-vascular bryophytes (mosses)


  • Mosses, hornworts and liverworts
    • Fossils of bryophyte spores ~470mya


  • Non-vascular; ground hugging carpets
    • bodies to thin to support height growth


  • Have a rhizoid but not a root
    • anchors plant
    • does not uptake water


  • Resistant spores

Bryophytes have gametophyte dominated life cycle